The International Primary CNS Lymphoma Collaborative Group (IPCG), formed at the 8th International Conference on Malignant Lymphomas in Lugano, Switzerland in June 2002, meets on a biannual basis and has attracted both a multidisciplinary and international membership. The primary objective of the IPCG is to advance the biological understanding, diagnosis and treatment of patients with primary central nervous system lymphoma (PCNSL). Topics of prior meetings have included: 1) Consensus guidelines for PCNSL clinical trials;2) Primary T-cell lymphoma of the nervous system;3) Low-grade CNS lymphoma. The goals of each thematic meeting are to review the preclinical and clinical science relevant to each topic;to produce multidisciplinary, collaborative research focused on each selected topic and, when appropriate, to disseminate scientific guidelines and methods for use by PCNSL researchers. Peer-reviewed publications have resulted from prior meetings including a vision statement for the IPCG;consensus guidelines for clinical trials in the PCNSL patient population;and a summary of the largest series of primary T-cell lymphomas of the nervous system published to date. Treatment-related neurotoxicity in PCNSL patients is the next major prospective IPCG project and will be the subject of the next scientific meeting. Attendance at IPCG meetings includes scientists, neuropsychologists and physicians from multiple specialties involved in every aspect of PCNSL clinical care and research. In addition, distinguished scientists and clinical investigators have been invited to the thematic sessions. Although the group has existed for only 3 years it have fostered international collaboration across multiple disciplines on an unprecedented scale and has had an impact on PCNSL research and clinical care.